This invention relates to ground control approach (GCA) systems and especially to the determination of the crab angle of an aircraft which is flying over a landing strip just prior to touching down.
GCA landing systems employ radar to guide an aircraft to a point about 4 seconds from touchdown. At this point, the radar loses altitude information because the radar cannot resolve the aircraft from its image in the ground. The landing systems also lack information about aircraft orientation so they cannot properly flare or decrab the aircraft prior to touchdown and must limit landings to low crosswind conditions. A GCA system which is able to determine crab angle a few seconds before touchdown so that the aircraft could be informed how much to change course to come in straight along the runway would thus provide a distinct improvement over present GCA systems.